ETC maintains thousands (and thousands) of drawings and we chose to maintain all of our drawing libraries in DWG format as it is not practical to maintain 2 versions of all drawing files.
In AutoCAD you can do a 'save as...' to save the drawing as a .DXF
If you are not working in AutoCAD, or another CAD application that is happy importing DWG's, you might look at DraftSight as a free file conversion tool:
http://www.3ds.com/products/draftsight/overview/
I primarily work in Vectorworks, but frequently use DraftSight to verify that DWG's and DXF's that have been exported from AutoCAD look the way they should after I import them.
